1. Field of the Invention
The present invention relates to a power receiving device and a power transmission device. In particular, the present invention relates to a power receiving device and a power transmission device between which power feeding is performed by using magnetic resonance. Further, the present invention relates to a power feeding system including the power receiving device and the power transmission device.
2. Description of the Related Art
A method called a magnetic resonance method attracts attention as a method for feeding electric power to an object (hereinafter, also referred to as a power receiving device) in a state where contact with a power supply source (hereinafter, also referred to as a power transmission device) is not made (such a method is also referred to as contactless power supply, wireless power supply, or the like). The magnetic resonance method is a method for forming an energy propagation path by providing resonator coupling between resonant coils each of which is provided in a power transmission device and a power receiving device. The magnetic resonance method has a longer power transmittable distance than other methods (e.g., an electromagnetic induction method and an electric field induction method). For example, Non Patent Document 1 discloses that in the magnetic resonance method, transmission efficiency is approximately 90% when the distance between a pair of resonant coils is 1 m and that the transmission efficiency is approximately 45% when the distance between the pair of resonant coils is 2 m.
In addition, a power feeding system capable of communicating between a power receiving device and a power transmission device has been developed. For example. Patent Document 1 discloses a power receiving device (power receiving unit) and a power transmission device (power feeding unit) having functions of feeding power with the use of the both of resonant coils (resonant elements) and power receiving (power transmission) coils (driven elements) and of communicating with the use of only the resonant coils. Specifically, the power receiving device and the power transmission device disclosed in Patent Document 1 include switches provided at one end and the other end of the resonant coil and at one end and the other end of the power receiving (power transmission) coil. By controlling switching of the switches by switching controllers, it is selected whether a power feeding function or a communication function is performed.